Synthesis and photophysical studies of non-covalently linked unsymmetrical porphyrins dyads and triads

Abstract

Non-covalent porphyrin dyads and triads containing N₃S porphyrin and RuN₄ porphyrin subunits were synthesized by treating meso-pyridyl-21-thiaporphyrin with RuTPP(CO)(EtOH) in toluene at refluxing temperature. The dyads and triads were characterized by various spectroscopic techniques and the properties were compared with the reported dyad containing N₄ and RuN₄ porphyrin subunits. The ¹H NMR study of dyads and triads indicated that the inner NH, β-heterocycle and meso-pyridyl protons of the 21-thiaporphyrin unit experienced large upfield shifts as compared to their corresponding monomeric meso-pyridyl-21-thiaporphyrins due to the ring current effect of RuTPP(CO) subunit. The singlet state photophysical properties of N₃S porphyrin subunit in dyads and triads showed 50-80 % quenching of fluorescence as observed previously for N₄-RuN₄ dyad due to heavy ruthenium ion(s).